The melanocyte-stimulating hormones are a class of peptide hormones that are produced by the intermediate lobe of the pituitary gland and regulate the synthesis of melanin.

Alpha Melanocyte-stimulating hormone belongs to a group called the melanocortins which includes ACTH, alpha-MSH, beta-MSH and gamma-MSH; these peptides are agonist peptide ligands for the melanocortin receptors and these are processed from the pre-prohormone proopiomelanocortin (POMC).

Alpha-MSH is the most important melanocortin for pigmentation. Substances that block the function of a-MSH are promising tools for the treatment of pigmentary disorders. Two examples of a-MSH blockers are the following:

Sophoraflavanone G

Sophoraflavanone G was also found to have an inhibitory effect on á-MSH-stimulated melanogenesis except tyrosinase inhibition.

Piperlonguminine

Piperlonguminine from Piper longum inhibited the á-MSH-induced melanogenesis with no effect on cell-free tyrosinase. Piperlonguminine inhibited the á-MSH-induced signaling that functioned through cAMP to the CREB that in turn regulates MITF and tyrosinase expression.

a-MSH synthetic analogues like afamelanotide and Melanotan II are also promising in the treatment of disorders of hypopigmentation.